Gate valves have long been used to control the flow of fluids through conduits having fluids passing therethrough. Examples include those shown by U.S. Pat. Nos. 3,029,060 and 3,770,247. Such valves include an apertured gate. The gate is caused to move, generally perpendicular to the direction of throughput flow. Such gates may be direct or reverse acting. Subsequently, actuators were developed, oftentimes using independent sources of power, such as pressurized gas, to effect such alignment and misalignment. Inasmuch as closing is absolutely necessary, in the event of line breaks, actuator-power failure, or the like, fail safe systems were desirable. Of late, governmental regulatory bodies have required such fail safe systems, for ecological protection purposes. Three particular problems have remained, namely, (1.) the desirability of an actuator being compatible with standard direct acting gates, (2.) the desirability of an actuator continuing to be functional where normal line pressure decreases with depletion of well pressure from which such line is supplied, and (3.) the necessity of causing the valve to close in the absence of pilot pressure. It was to solve such problems that this invention was directed.